# Ampmeter help

Discussion in 'Irrigation' started by EagleLandscape, Nov 16, 2007.

1. ### EagleLandscapeLawnSite Platinum MemberMale, from Garland, TexasPosts: 4,347

I just bought an amp meter / multi meter deal for this xmas light install i have tomorrow. i had a regular multi meter, but nothing that could read amp load.

its a sperry dsa-500

I'm trying to read the amp draw on this power strip next to my desk, and I have it on the 40A setting (vs the 400A setting) and i have the line running through like the manual suggests, (line over left clamp, and under right clamp,) but im not getting a reading.

am i missing something?

2. ### DavidS1964LawnSite Memberfrom Richmond VirginiaPosts: 36

You need a line seperator. Grainger has them for about \$15.00.It splits your two main wires. The black or white wire. Once you spit the wires you can measure the amperage. You can also just add all of the appliances together. The amperage is written on the back of the appliance.

P.S It is possible to use your other meter. You just kinda had to hold it in your hand.

3. ### wab1234LawnSite Memberfrom fall river maPosts: 48

you can only have a single wire going thru the clamp, more than one and they cancel each other out similar to positive and negative charges with a magnet. the only way to use a meter without an amp clamp is to use ohms law. This states that amps equals volts divided by volts. I might have this backwards there is a book/bible called "UGLIES" which tells the true ohms law and everything else about the N.E.C. which might be helpful when doing any electrical work.

4. ### KirilLawnSite Fanaticfrom District 9 CAPosts: 18,308

Ohm's Law -> I = V/R
Units: I = Amps V = volts R = ohms

Where a voltage of 1 V across a conductor causes a current of 1 A to the flow through it, resistance is 1 ohm

5. ### wab1234LawnSite Memberfrom fall river maPosts: 48

Thank you kiril volts divided by volts doesn't make sense. I hope the rest was a little easier to understand

6. ### DavidS1964LawnSite Memberfrom Richmond VirginiaPosts: 36

W1234 you are incorrect about the only way is to use a multimeter with the clamp on ends for amperage. If you look at a regular meter without the clamp on ends there are some that have the current symbol on them. They will read amperage also. The current will pass through the leads. Usualy they are low current meter readers. Also if you have the wattage which is usualy on the back of all appliances and you know the voltage Dah!!. Voltage time amperage gives you wattage. So wattage dived by voltage gives you amperage.

7. ### KirilLawnSite Fanaticfrom District 9 CAPosts: 18,308

The correct formula for determining electrical work is:

W = IVt = (V^2/R)t = I^2Rt (where W is expressed as 1 Wattsecond = 1 Joule = 1 Nm)

And for determining electrical power:

P = V^2/R = I^2R (where P is expressed as watts)
V = P/I

As you can see in the second set of formulas, your method of determining wattage and voltage is incorrect.

8. ### KirilLawnSite Fanaticfrom District 9 CAPosts: 18,308

Edit above -> your method is correct when using V = P/I where 1 V = 1 W/A.

Sorry, got side tracked by the attitude and poor spelling.

9. ### Ground MasterLawnSite Senior Memberfrom colorado springsPosts: 505

John - get a 2' long extension cord. Carefully cut off several inches of the outside cover to expose the 3 wires. You'll then be able to clamp on to 1 individual wire to read the amp load. Just be very careful with the exposed wiring